1. Field of the Invention
The invention relates to a silicon semiconductor substrate and a method of fabricating the same, and more particularly to a silicon substrate including a defective layer to which gettering is carried out.
2. Description of the Related Art
As devices are formed on silicon substrate in smaller size and in higher integration, it becomes more important to prevent performance deterioration of devices caused by heavy metals intruding into a device during fabricating process, and fabrication yield deterioration. Thus, a technique for removing heavy metals out of a device formation region has been developed. Such a technique is called gettering technique. In general, gettering techniques can be grouped into intrinsic gettering and extrinsic gettering. In intrinsic gettering (IG), precipitation of oxygen contained in silicon and crystal defects caused by such precipitation act as a capturer of heavy metals. Extrinsic gettering is further grouped into BD, PDG and PG. In a so-called BD technique, crystal defects caused by artificially given mechanical damages act as a capturer of heavy metals. In phosphorus gettering (PDG), heavily phosphorus-doped diffusion layer acts as a capturer of heavy metals. In polysilicon gettering (PG) technique, a polysilicon layer formed on a bottom surface of a silicon substrate acts as a capturer of heavy metals.
For instance, Japanese Unexamined Patent Publication No. 3-238825 has suggested extrinsic gettering in which a carbon-doped polysilicon layer formed on a bottom surface of a semiconductor substrate is used to capture heavy metals. For another instance, Japanese Unexamined Patent Publication No. 2-47836 has suggested another extrinsic gettering in which a supersaturated oxygen-doped polysilicon layer is formed at a bottom surface of a semiconductor substrate for capturing heavy metals. In these extrinsic gettering techniques, carbon and oxygen contained in each of the polysilicon layers are diffused in a silicon semiconductor substrate. The thus diffused oxygen and carbon facilitate precipitation of oxygen contained in a substrate to thereby carry out gettering for capturing heavy metals.
Conventional intrinsic gettering has problems in that mechanisms for precipitating oxygen include extremely various and complicated factors, and it is quite difficult to completely control oxygen precipitation with the result of insufficient formation of a defective layer, and that there occurs defectiveness in a device formation region which should not have any defectiveness, thereby a production yield of a semiconductor device being reduced. Other problem is that mechanical strength of a silicon semiconductor substrate is remarkably reduced by reduction in interstitial oxygen concentration and occurrence of dislocation accompanied with oxygen precipitation, when oxygen is much precipitated, thereby there occurring a slip in a silicon semiconductor substrate during semiconductor device fabrication process, resulting in reduction in production yield of a semiconductor device.
Extrinsic gettering has a problem that crystal defects and crystal grains of polysilicon both acting as a core for gettering are eliminated in thermal treatment carried out during semiconductor device fabrication process, or crystal grains of polysilicon are grown up, and hence the gettering effects cannot last until the semiconductor device fabrication process is completed.
In the method of facilitating precipitation of oxygen contained in a substrate by means of supersaturated oxygen-doped polysilicon layer as suggested in the above mentioned Publication No. 2-47836, there can be obtained only small gettering effects against heavy metals when the oxygen concentration is low. In the method of facilitating precipitation of oxygen contained in a substrate by means of heavily oxygen- or carbon-doped polysilicon film as suggested in the above mentioned Publication No. 3-238825, similarly to the above mentioned intrinsic gettering, mechanical strength of a silicon semiconductor substrate is remarkable reduced by occurrence of dislocation accompanied with oxygen precipitation out of a silicon semiconductor substrate, thereby slip occurring in a silicon semiconductor substrate during semiconductor device fabrication process, resulting in reduction in production yield of a semiconductor device.